I agree with others who have said that this quote minimizes the pain and suffering associated with depression. I do think, however, that this quote gets at something which may be true for some people: that depression can serve a function, in this case, causing an individual to step back and process or analyze the things that are happening in life. I guess I view it as the opposite of "rest", more like painful hard-thinking, and this won't be true for all people.
In evolutionary psychology, there's a theory (eg. "analytical rumination hypothesis") that depression exists as the body's response to problems which require complex analysis. It effectively causes a person to step back and focus on the problem. This doesn't mean that the experience isn't painful, but just that it serves a purpose for some people. I certainly wouldn't call that "rest" though.